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Conducting Life Cycle Assessments
which functions they should have and how differences are taken into consideration in the
case where one product has more functions than the other.
2.1.2.2 Functional Unit
The functional unit is the quantified definition of the function of a product. For example, the
functional unit of an aluminum beverage can might be defined as packaging 330ml of
beverage, protecting it from UV radiation and oxidation and keeping in the carbonic acid
for at least half a year. The ability to drink the beverages directly out of the packaging
might be an additional function which should be taken into account.
In order to compare two products, their functional units must be equivalent. For example,
both glass bottles and cartons are used for milk packaging. Since the most common size
for each packaging type might differ, the functional unit is set to be the packaging for 1000
liters of milk in order to compare the two packaging systems properly.
Defining the functional unit can be difficult because the performance of products is not
always easy to describe or isolate.
Part of defining a functional unit is the definition of a reference flow. The reference flow is
the measure of product components and materials needed to fulfill the function, as defined
by the functional unit. All data collected during the inventory phase is related to the
reference flow. In other words, all data used in the LCA must be calculated or scaled in
accordance with this reference flow.
2.1.2.3 System Boundaries
The system boundary defines which processes will be included in, or excluded from, the
system; i.e. the LCA.
It is helpful to describe the system using a process flow diagram showing the processes
and their relationships. Figure 3 shows a generic process flow diagram with all processes
included in the LCA shown inside the box marked as the System Boundary.
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